FIG. 8 is a cross-sectional view showing a conventional plasma CVD apparatus in outline. FIG. 9 is a front view showing an aperture plate. The aperture plate 107 is a component for narrowing an electron beam in an electron microscope. The plasma CVD apparatus shown in FIG. 8 is an apparatus for forming a metal film on the surface of the aperture plate 107.
As shown in FIG. 8, the conventional plasma CVD apparatus has a chamber 101, and, in the chamber 101, a gas shower electrode 102 as an upper electrode of a parallel flat plate type and a lower electrode 103 are arranged. The gas shower electrode 102 is connected to a raw material gas supply source 104. Moreover, the gas shower electrode 102 and the chamber 101 are connected to the ground potential.
On the lower electrode 103, a substrate 106 is placed, and on the substrate 106, the aperture plate 107 is attached. To the lower electrode 103, a radio frequency power source (RF power source) 109 is connected via a matching box 108.
The aperture plate 107 shown in FIG. 9 is a plate-like member having a thickness of 10 to 500 μm, and has a first through hole (a through hole for the attachment) 107a with a diameter of around 2 mm. Moreover, for the aperture plate 107, a plurality of second through holes (not shown) with a diameter of around 2 to 100 μm is arranged, wherein the second through hole is a hole for narrowing the electron beam in an electron microscope. The portions for which the formation of the metal film is necessary in the aperture plate 107 are a portion located near the second through hole on the front and back surfaces of the aperture plate, and the inside surface of the second through hole.
A method of forming the metal film on the aperture plate 107 using the above conventional plasma CVD apparatus is as follows.
On the substrate 106 such as a wafer, the aperture plate 107 is attached, and the substrate 106 is placed on the lower electrode 103 in the chamber 101. Subsequently, a raw material gas is supplied to the gas shower electrode 102 from the raw material gas supply source 104, and the raw material gas is ejected from the gas shower electrode 102 in a shower shape toward the lower electrode 103. Then, by outputting a radio frequency wave from the RF power source 109 to the lower electrode 103 via the matching box 108, a metal film is formed on the surface of the aperture plate 107 and the inside surface of the second through hole by a plasma CVD method.
After that, the substrate 106 is taken out of the chamber 101, the aperture plate 107 is peeled off from the substrate 106 and attached on the substrate 106 so that the other surface (the back surface) of the aperture plate 107 is exposed, and the substrate 106 is placed on the lower electrode 103 in the chamber 101. After that, by the same method as that for forming the metal film on the front surface of the aperture plate 107, the metal film is formed on the back surface of the aperture plate 107 and the inside surface of the second through hole.